2, 3-bis-(difluormaino)-butane-1, 4-diisocyanate and polyurethanes prepared therefrom



United States Patent 3,390,136 2,3 BIS (DIFLUORAMINO) BUTANE 1,4-

DIISOCYANATE AND POLYURETHANES PREPARED THEREFROM Ralph J. Leary, Cranford, Eugene L. Stogryn, Fords, and Perry A. Argabright, Cranford, NJ., assignors to Esso Research and Engineering Company a corporation of Delaware No Drawing. Filed Nov. 20, 1961, Ser. No. 154,391 3 Claims. (Cl. 26077.5)

ABSTRACT OF THE DISCLOSURE The compound 2,3-bis-(difluoramino)-butane-1,4-diisocyanate is prepared by addition react-ion of 2-'butene-1,4- diisocyanate with N F and is useful for producing highenergy polyurethanes.

This invention is concerned with a high-energy polyurethane binder containing a high proportion of NF groups for use in solid rocket propellants, and is concerned with preparation of the binder from a suitable diisocyanate monomer condensed with a suitable diol monomer, :both kinds of monomers containing oxidizing groups.

Polymeric binders containing oxidizing constituents which are compatible with high-energy propellant ingredients and that can be cast into a solid grain have been diificult to find. One reason for this difiiculty is that some polymers have to be heated to a high melting or softening temperature for compounding and casting. At high temperatures, the CNF groups tend to decompose. Another difficulty arises in forming orcasting a condensation polymer which splits out gaseous decomposition products, e.g., H O or HCl. Still another difiiculty in obtaining a suitable binder is that of obtaining one which has suitable flexibility, toughness and adhesive properties. The major difficulty in forming polymeric binders containing NF groups is the strong tendency of the NF group to deactivate the catalyst and thereby inhibit polymerization.

A discovery enabling the present invention which overcomes difiiculties mentioned is the synthesis of the NF containing diisocyanate, which may be named 2,3-bis- (difluoramino)-butane-1,4-diisocyanate, which has the following formula:

OCNCH CH (-NF CH (NF CH NCO This diisocyanate satisfactorily reacts at mild temperatures with NF -containing glycols to form polyurethanes having a high proportion of NF groups. This diisocyanate has been reacted satisfactorily with glycols containing high-energy groups such as NF and N0 In preparing a castable binder, the polyurethane binder lends itself to crosslinking which is advantageous in formulation of solid propellant mixtures.

To synthesize the NF -containing diisocyanate, it has been found desirable to derive 2-butene-1,4-diisocyanate having the formula OCNCH CH=CHCH NCO from 3- hexene-l,6-dioic acid chloride which is obtained from 1,3- butadiene as an inexpensive, high-purity starting material. The 1,3-butadiene is easily converted to 1,4-dichlorobutene-2 by chlorination and this dichlorobutene compound is converted readily to the dinitrile, 1,4-dicyanobutene-2. The dinitrile is hydrolyzed to 3-hexene-1,6-dioic acid which is reacted with SOCl to form 3-hex-ane-l,6- dioic acid chloride. Said acid chloride is reacted with sodium azide (NaN in an inert organic solvent immiscible with water, such as benzene, to form 3-hexene-1,6 dioic acid azide, which acid azide in an organic solvent free of water is decomposed thermally to form the 2- butene1,4-diisocyanate which can then be recovered by separation of the solvent.

3,390,136 Patented June 25, 1968 ice EXAMPLE 1 2-butene-1,4-diisocyanate adds a theoretical amount of NF, groups across the double bond when reacted at about 100 C. for 5 hours in CCl, under 400 to 450 p.s.i. of N F The temperature, time, solvent and pressure may be varied as, for example, in the use of a reaction temperature of 80 C. fora period of 15 hours. The carbon tetrachloride or similar kind of solvent may be evaporated with a stream of nitrogen to remove the solvent from the adduct. The adduct residue may then be distilled under vacuum, e.g., 0.001 mm. Hg absolute with a heating bath temperature of C. The recovered reaction product, a water-white adduct, was analyzed as follows:

Theory for C H O N F C, 29.75%; N, 23.16%; F, 31.4%. Found: C, 31.9%; N, 23.18%; F, 31.3%.

The infrared spectrum and nuclear magnetic resonance spectrum of the adduct showed it contained the terminal isocyanate groups and the NF groups. The structure of the adduct, consistent with the elemental and structural analyses, is as follows:

OCN-CHzCH-CHCHg-NCO NF, NF;

It was found that care had to be taken to avoid excessive rise in the reaction temperature to avoid decomposiwherein R represents a hydrocarbon group having attached energy groups such as NF and N0 and R' represents the hydrocarbon group having attached NF groups in the diisocyanate.

Equimolar proportions of the diisocyanate and of the glycol are mixed in an inert atmosphere and heated at about 40 to 50 C. for about 1 hour to obtain the copolymerization or condensation reaction. This reaction forms a viscous prepolymer, the property of which allows one to admix therewith other ingredients such as other solid fuel, solid or liquid oxidizer, liquid plasticizer and crosslinking agents. The prepolymer blend is then treated with a catalyst. Catalysts generally useful in the curing are salts of heavy metals, e.g., ferric chloride and ferric acetyl acetonate. Fortunately, the prepolymer can be cured at ambient temperatures, e.g., 20 to 25 C., for 24 to 48 hours or at a higher temperature, e.g., 50 C., for about 8 to 24 hours.

The resulting cured polymer does not shrink and clings tenaciously to the walls of the reaction vessel, thus indicating it has good case bonding properties.

liii,390,186

3 The condensation of the diisocyanate-NF adduct with an available energetic glycol was demonstrated using 11,2- dinitropropane diol. This condensation reaction is represented by the following equation:

Analyses.Found: N, 20.8%; F, 37.2%. Theory: N, 20.9%; F, 37.8%.

Another solid polyurethane containing NF; groups was formed using the N 12, adduct of 2-butene-1,4-diol.

EXAMPLE 3 The N F adduct of 2-butene-1,4-diisocyanate was reacted in an equimolar proportion with the N 1 adduct of 2-butene-1,4-diol using the procedure that has been described. The N F adduct of the diol has the following formula:

HOCH CH (NF CH (NF CH OH Analyses.-Found: C, 27.87%; N, 19.69%: F, 36.8%. Theory: C, 27.70%; N, 19.38%; F, 35.1%. Moi. weight, 1,200. Inherent viscosity in methanol, 0.058.

EXAMPLE 4 The N F adduct of Z-butene-l,4-diisocyanate was reacted in an equimolar proportion with the iii-N 1 adduct of 3,4-dihydroxy-1,5-hexadiene under the conditions outlined in Example 1 to give a tacky solid polyurethane.

Analyses.--Fund: N, 19.1%; F, 41.9%. Theory: N. 19.9%; F, 40.5%. Mol. weight, 835. Inherent viscosity in methanol, 0.06.

The recurring unit characterizing the polyurethane product contains the constituents of the diisocyanate and of the diol in the recurring units.

The NF -containing polyurethanes which have been prepared show a good degree of impact stability, in the range of to about 50 kg. in.

The energetic (NF -containing) polyurethane prepolymers of 2,3-bis-(NF )-butane-1,4-diisocyanate have a suitable consistency and compatibility with energetic fuels and oxidizers, e.g. powdered metals, boron, lithium, beryllium, magnesium, aluminum and hydrides, hydrazinium nitroformatc, hexanitroethane, tetrakis-(NF tetrahydrofuran, and tetrakis-(NFQ-butane. This is an important qualification in formulating solid propellants of suitably blended ingredients that confer on the composited propellants desired high-energy values in terms of specific impulse and uniform combustion.

Satisfactory castable blends have been made with the described (NF )-containing polyurethane prepolymers formed to have molecular weights in the range of about 835 to 1350, as in the following formulation:

Ingredient: Wt. percent Tetrakis-(NF )-tetrahydrofuran 50 Hydrazinium nitroformate -35 Boron powder 0-5 Polyurethane binder (Example 1) 15 Isp=280.

The blending of the ingredients was conducted safely and without noticeable decomposition or loss of materials. The blend described was cast and cured. The cast and cured composite showed tenacious adhesion to rocket motor wall materials.

The invention described is claimed as follows:

1. 2,3-bis-(difluoramino)-butane-1,4-diisocyanate.

2. A process for preparing 2,3-bis-(difluoramino)- butane-1,4-diisocyanate comprising reacting 2-butene-1,4- diisocyanate with N F under pressure at a temperature of about 20 C. to 150 C.

3. The polyurethane product having a molecular weight between 835 and 1350 formed by reacting 2,3-bis- (difluoramino)-butane-1,'4-diisocyanate with 2,2-dinitropropane-1,3-diol in about equal proportions in an inert atmosphere for a period of about 1 hour at 40 C. to C.

References Cited Polymer Previews, vol. 3, Issue 6, June 1967, p. 298 cited as being of interest.

American Chemical Society, Abstracts of Papers, Aug. 22, 1966, Items 4 and 18 in Section K cited as being of interest.

Chemical Abstracts, vol. 65, p. 10482 (1966).

DONALD E. CZAJA, Primary Examiner.

R. L. CAMPBELL, Examiner.

J. W. WHISLER, F. MCKELVEY, Assistant Examiners. 

